The "beads-on-string" structure seen under an electron microscope refers to?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Ribosomes on mRNA
• Nucleosomes in Chromatin
• Proteins on DNA
• Genes on Chromosome
Correct Option: B  [ Nucleosomes in Chromatin ]

Remark: Chromatin fibers viewed under an electron microscope appear as beads on a string, where the beads are nucleosomes and the string is the linker DNA.

Which scientist(s) conducted the "Transforming Principle" experiment?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Frederick Griffith
• Hershey and Chase
• Meselson and Stahl
• Avery, MacLeod, and McCarty
Correct Option: A  [ Frederick Griffith ]

Remark: Frederick Griffith conducted the experiments with Streptococcus pneumoniae and mice in 1928, discovering the Transforming Principle.

In Griffith's experiment, mice died when injected with?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Live R strain
• Heat-killed S strain
• Heat-killed S strain + Live R strain
• Heat-killed R strain
Correct Option: C  [ Heat-killed S strain + Live R strain ]

Remark: Mice survived injection with heat-killed S strain alone and live R strain alone. However, the mixture of both caused death because the R strain was transformed into virulent S strain by DNA from the heat-killed S strain.

The S-strain of Streptococcus pneumoniae is virulent because?

[Molecular-Basis-of-Inheritance] [class-xii ]

• It lacks a capsule
• It has a polysaccharide coat
• It is a virus
• It produces a toxin
Correct Option: B  [ It has a polysaccharide coat ]

Remark: The S-strain (Smooth) possesses a smooth polysaccharide mucous coat that protects it from the host's immune system, allowing it to cause pneumonia.

Avery, MacLeod, and McCarty proved that the transforming principle was?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Protein
• RNA
• DNA
• Polysaccharide
Correct Option: C  [ DNA ]

Remark: They purified biochemicals from the heat-killed S cells and found that only DNA—and its digestion by DNase—prevented transformation, proving DNA was the transforming agent.

Why was the Hershey-Chase experiment considered the "unequivocal proof" of DNA as genetic material?

[Molecular-Basis-of-Inheritance] [class-xii ]

• It used bacteria
• It used viruses
• It ruled out protein using radioisotopes
• It was done later
Correct Option: C  [ It ruled out protein using radioisotopes ]

Remark: By using radioactive Sulfur (for protein) and Phosphorus (for DNA), they showed conclusively that only DNA enters the bacterial cell to direct viral reproduction, ruling out protein entirely.

In the Hershey-Chase experiment, radioactive Sulfur-35 labeled the?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Viral DNA
• Viral Protein Coat
• Bacterial DNA
• Bacterial Cell Wall
Correct Option: B  [ Viral Protein Coat ]

Remark: Sulfur is present in amino acids (cysteine, methionine) found in proteins but not in DNA. Thus, S-35 labeled the viral protein capsid.

Radioactive Phosphorus-32 labels DNA because DNA contains?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Sulfur
• Phosphates
• Amino acids
• Ribose
Correct Option: B  [ Phosphates ]

Remark: DNA contains a phosphate backbone. Phosphorus is not found in proteins (usually). Thus, P-32 specifically labels DNA.

Which step involves the agitation of viral coats from bacterial cells in the Hershey-Chase experiment?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Infection
• Blending
• Centrifugation
• Transformation
Correct Option: B  [ Blending ]

Remark: Blending is the mechanical agitation step used to shear off the empty viral protein coats (capsids) from the surface of the bacterial cells after infection.

The genetic material in Tobacco Mosaic Virus (TMV) is?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Double-stranded DNA
• Single-stranded DNA
• RNA
• Protein
Correct Option: C  [ RNA ]

Remark: TMV is a classic example of a virus that uses RNA as its genetic material, alongside QB bacteriophage.